Texture export to dae setting or procedural issues
I don't know if you resolved this in the end.   I am having the same problem with the png texture files.  After trying lots of different things, I looked inside the dae file from the zenka site and noticed that it was not made using blender but with 3D Studio Max - so no wonder the instructions didn't work.  

I also found this post http://rowanpeter.com/amidoinitrite/a-simple-cube-blender-2-62-and-aurasma-studio/  His dae file is made using blender but again the png texture files do not seem to be recognised by aurasma (or don't anymore, he has provided video evidence that it worked at some point.)

Sorry this isn't really an answer, but I thought knowing that the zenka file was not made with blender might help you.   

If you did find a solution I would be grateful if you could share it with me.  I'll let you know if I have any luck myself!